Wireless-based battery powered field routers and field devices are utilized in a variety of wireless industrial applications such as critical remote monitoring required industrial plants and facilities. Such wireless devices may employ communications protocols and networks such as, for example, TDMA, COMA, GSM, WiFi, etc.
Field devices are used in industrial processes to control or monitor operation of the process. Wireless field devices can measure any of a number of process characteristics such as, for example, pressure, level, flow velocity, mass flow, pH, temperature, density, and conductivity or can monitor process equipment for such things as vibration, strain or corrosion or can monitor the general plant environment for such things as fire and gas detection or can be used for locating the present position of workers and equipment. For example, a process variable transmitter is a type of field device which can be used to monitor a process variable of a process fluid. Examples process variables include temperature, pressure, level, flow rate, etc. A controller is a type of field device which is used to control operation of the process. For example, the controller can control a flow rate of a process fluid by adjusting a position of a valve in a pipe carrying the fluid.
The ability to resolve problems observed in estimating battery capacity and battery capacity remaining are critical in, for example, TDMA based battery powered field routers/field devices for wireless industrial applications. Battery draining in field devices does not follow a linear curve when plotted, for example, with respect to battery voltage versus time scale. Rather, such data indicates a very negligible drop in the beginning when the battery voltage is high and drops drastically close to the end of the battery life. Using traditional method to detect the battery voltage level using, for example, a DAC (Digital-to-Analog Converter) circuit in the microcontroller does not help the end user as the remaining battery voltage drops down to very low with a short span of time and the user or customer will not have enough time to replace the batteries once an alarm is generated by the system due to the nature of the battery voltage reduction.
Conventional DAC based battery measurement techniques read the battery voltage and report the battery voltage. Potential problems with DAC based voltage measurement techniques include, for example, issues related to the fact that a typical field device may indicate a lower battery for only a short duration before draining completely, which unfortunately impacts the drop-offs associated with the wireless field device(s), which may be monitoring, for example, critical industrial plant parameters. Additionally, field devices are used to monitor plant critical parameters. Thus, the end user must be very vigilant for low battery alarms, which eventually may result in wireless field devices drop-offs in industrial applications if neglected. Plant operations can therefore be negatively impacted simply due to a failure to monitor lower battery alarms. Additionally, the DAC based technique of battery measurement will not be able to show the battery remaining in terms of percentage or days left due to the sudden fall of battery characteristics. Solutions are therefore presented herein to these and other problems inherent with present battery monitoring and measurement techniques.